1. Technical Field
The present invention relates to a method of extending a life expectancy of a high-temperature piping such as a high-temperature piping and a pressure vessel, for example, used in thermal and nuclear power plants, chemical plants and the like, and a life expectancy extension structure of a high-temperature piping.
2. Description of the Related Art
Since, for example, a boiler or the like constituting a thermal power plant is operated under a high-temperature and high-pressure environment, damage due to creep or the like may accumulate in a heat-resistant steel as a material forming the boiler, by being operated over a long term. Accordingly, at the time of operation of this type of plant, it is important to maintain the reliability of a pressure-resistant unit by performing the highly accurate life expectancy evaluation of the heat-resistant steel in ensuring a stable operation over a long term.
Although a high-temperature piping used in a thermal power plant or the like has a function of carrying steam heated in the boiler to a steam turbine, a creep damage progresses due to the high-temperature and the long-term use and a creep void occurs, a crack occurs due to continuous voids, and finally, the piping breaks.
In order to prevent the final breakage, a degree of creep damage of each member is derived by analyzing a degree of growth of the creep void through a regular non-destructive inspection, thereby performing the remaining life expectancy evaluation of the member (see Japanese Laid-open Patent Publication No. 2004-85347; and Japanese Laid-open Patent Publication No. 2008-122345). Since there is a high risk of creep rupture of the piping welded portion in general compared to a base metal, a position to be inspected is mainly a welded portion.